Optical disk apparatus wherein recording clock signal is stopped being supplied to semiconductor laser drive circuit on optical pickup during reproduction operation

ABSTRACT

According to the present invention, in an optical disk apparatus constructed to supply signals for controlling a semiconductor laser drive circuit provided to an optical pickup from a signal processing circuit through a flexible cable, the semiconductor laser drive circuit is so constructed as to generate a drive current signal for the semiconductor laser on the basis of a binary signal and a clock signal which are supplied from the signal processing circuit through the flexible cable and the signal processing circuit is so constructed as to stop supplying the block signal to the semiconductor laser drive circuit through the flexible cable during reproduction of data, and to start supplying the clock signal to the semiconductor laser drive circuit before recording of data.

This application is a continuation of application Ser. No. 09/463,007filed on Jan. 19, 2000, U.S. Pat. No. 6,552,987 which is a nationalstage application under 35 USC 371 of international application No.PCT/JP99/04114 filed on Jul. 30, 1999.

TECHNICAL FIELD

The present invention relates to a technique of recording andreproducing information on and from an optical disk representing arecording medium, and more particularly, to an information recording andreproducing technique which can prevent S/N degradation in areproduction system due to cross talk with the reproduction systemcaused by circuit operation in a recording system when the information(inclusive of address information recorded on the recording medium inadvance) is read out of the recording medium.

BACKGROUND ART

In the field of products concerning the optical disk such as CD, DVD andthe like, an increase in capacity of the optical disk and an increase inspeed of data transfer in an optical disk apparatus have recently beendesired more and more. Also, with the capacity of the optical diskincreased, mark and space (corresponding to 1, 0 of information) to beformed on the optical disk are required to be finer and formation ofsuch fine mark and space is required in the optical disk apparatus.

In order to form accurate and fine mark and space, one mark recordingwaveform is required to have a multi-pulse form in a drive currentwaveform for a semiconductor laser during recording and a pulse positionor pulse width at the mark start end and a pulse position or pulse widthat the mark termination end must be controlled adaptively in accordancewith a mark length of its own and an adjoining space length. Forexample, in a DVD-RAM, the aforementioned adaptive control of the pulseposition or pulse width is required to be performed in T/16 to T/32steps (T being a minimum unit for determining the mark and space lengthsand corresponding to the period of a so-called channel clock chCLK).

Further, the drive current waveform is also needed to be quaternary incontrast to the conventional binary and so has become complicated. Inaddition, with the data transfer speed increased, the frequency of theaforementioned drive current waveform has become higher.

As the capacity and data transfer speed increase in this manner, currentat multiple-valued levels supplied to the semiconductor laser must beswitched at a high speed. To assure such a high-speed current switchingcharacteristic as above (rise characteristic: Tr characteristic and fallcharacteristic: Tf characteristic of the drive current), it ispreferable that the semiconductor laser drive circuit be disposed in theproximity of the semiconductor laser.

To meet this requirement, a conventional semiconductor laser drivecircuit is so constructed as to have a plurality of current sources atleast one of which is externally selected to drive the semiconductorlaser. Therefore, as the drive current waveform has multiple-valuedlevels, the number of control signal lines for selecting the currentsource increases. Further, when the semiconductor laser drive circuit iscarried on an optical pickup, control signals are supplied through aflexible cable, facing a difficulty that because of dullness of thecontrol signal waveforms and the difference (skew) in delay amountbetween control signals, the accurate drive current waveform cannot beobtained.

As an optical disk apparatus for solving the difficulty as above, thepresent applicant has proposed an optical disk apparatus described inJapanese Patent Application No. 10-206083 filed on Jul. 22, 1998, whichwas published on Oct. 15, 1999, as Japanese Patent Application Laid-OpenNo. 11-283249.

A semiconductor laser drive circuit shown in Japanese Patent ApplicationNo. 10-206083 is comprised of drive waveform information memory meansfor storing one or more information of drive waveform which drives asemiconductor laser in compliance with a binary recording signal (forexample, NRZ signal) to be recorded on a recording medium, drivewaveform decoding means for decoding the drive waveform on the basis ofthe information stored in the drive waveform information memory means,means for generating an address for selecting the drive waveforminformation of the drive waveform information memory means on the basisof the binary recording signal, control means for storing the externallysupplied drive waveform information in the drive waveform informationmemory means, and n-multiplying means (so-called PLL) for n-multiplyinga clock signal CLK supplied through a flexible cable to deliver achannel clock signal chCLK and supplying the channel clock signal asoperation clock signal for the address generation means and the drivewaveform decoding means.

The drive waveform decoding means generates timing signals for N equaldivision (for example, 16 or 32 equal division in the DVD-RAM) of theperiod T of the chCLK by using a delay line on the basis of the channelclock signal chCLK delivered out of the n-multiplying means, thuspermitting the aforementioned control of the pulse width or pulseposition.

With this construction, when the drive waveform information is stored inthe drive waveform information memory means in advance through thecontrol means, the drive current waveform is generated during recordingby supplying the binary recording signal (NRZ), the clock signal CLK anda signal WRgate for control of the recording or reproducing operationmode to the semiconductor laser drive circuit carried on the opticalpickup through the flexible cable, so that the semiconductor laser canbe driven nearby and the difficulty of the conventional example that thedrive current waveform is distorted owing to the dullness or skew of thecontrol signals on the flexible cable can be eliminated to therebyassure desired Tr and Tf characteristics.

In case the multiplying number n of the n-frequency means is set to 4,the frequency of the clock signal CLK equals ¼ of the chCLK and ascompared to the conventional example (the current source selectingsignal having the same frequency as chCLK must be supplied), thefrequency of the control signals on the flexible cable can be reduced to¼ as compared to the conventional example and the EMI generated from theflexible cable can be reduced. To add, in the DVD-RAM, the frequency ofthe NRZ signal (repetition of 3T length mark and 3T length space gives amaximum frequency) is ⅙ of the channel clock signal chCLK.

As the capacity of the optical disk increases (densifying), however, thelevel of the reproduction signal for reading information from therecording medium decreases and for the sake of assuring reliability ofreproduction data, the influence such as cross talk from the recordingcircuit system to the reproduction circuit system must be moredecreased. The optical pickup carries photodetectors for detecting areflection light beam from the optical disk and I-V amplifiers forconverting output currents of the photodetectors to voltages, andoutputs of the amplifiers are supplied to a read channel LSI and thelike through the flexible cable. Accordingly, the influence of thecrosstalk from the recording circuit system to the reproduction circuitsystem must be reduced on the flexible cable to prevent degradation ofthe reproduction S/N.

Especially, when a sector is defined as a unit of recording (storage of2 Kbyte user data) as shown in a DVD-RAM (2.6 GByte) illustrated at (1)in FIG. 4 and physical address information of each sector in the form ofpits is recorded on the head of each sector (this area is called PID),the PID must be reproduced sector by sector to confirm the address andthen data to be recorded on a user data area of each sector must berecorded. In other words, even during recording of data, not onlyrecording of data is carried out but also recording and reproduction ofdata is carried out repetitively.

When, as in the case of the semiconductor laser drive circuitconstructed as above, the supply of clock signal CLK to thesemiconductor laser drive circuit by way of signal lines such as theflexible cable (hereinafter simply referred to as “flexible cable”) iskept even during PID reproduction as shown at (4) in FIG. 4 by takingstability of the frequency of the clock signal chCLK (output signal ofthe n-multiplying means) during user data recording following the PIDinto consideration, EMI of the clock signal CLK on the flexible cable(unwanted radiation emitted by the clock signal on the flexible cable)runs in a read signal (at (5) in FIG. 4) on the same flexible cable oron a flexible cable of the separately provided photoelectric conversioncircuit to cause crosstalk, giving rise to a problem that the S/N of thereproduction signal is degraded.

An object of the present invention is to decrease leakage of the EMI ofthe clock signal necessary for recording of data to the reproductionsignal and degradation of the S/N of the reproduction signal due tocrosstalk and to suppress an increase of the EMI level which causes theS/N degradation of the reproduction signal.

DISCLOSURE OF INVENTION

To accomplish the above object, according to the present invention, anoptical disk apparatus comprises a semiconductor laser drive circuithaving LD recording drive current waveform generating means forgenerating a recording drive current waveform for a semiconductor laserby using a clock signal chCLK as operation clock when recordinginformation on a recording medium and reproduction drive current supplymeans for supplying a reproduction drive current to the semiconductorlaser when reading the information from the recording medium, recordingclock supply means for supplying the clock signal chCLK to thesemiconductor laser drive circuit, recording/reproduction mode controlmeans for controlling recording/reproducing operation of thesemiconductor laser drive circuit, and clock stop means for stopping thesupply of the clock signal chCLK from the recording clock supply meansto the semiconductor laser drive circuit when the output of therecording/reproduction mode control means designates reproducingoperation.

Also, to accomplish the above object, according to the presentinvention, an optical disk apparatus comprises a semiconductor laserdrive circuit having multiplying means for providing a clock signalchCLK which is n times (n being positive integer) the frequency of aclock signal CLK, LD recording drive current waveform generating meansfor generating a recording drive current waveform for a semiconductorlaser by using the clock signal chCLK as operation clock when recordinginformation on a recording medium and reproduction drive current supplymeans for supplying a reproduction drive current to the semiconductorlaser when reading the information from the recording medium, recordingclock supply means for supplying the clock signal CLK to thesemiconductor laser drive circuit, recording/reproduction mode controlmeans for controlling recording/reproducing operation of thesemiconductor laser drive circuit, and clock stop means for stopping thesupply of the clock signal CLK from the recording clock supply means tothe semiconductor laser drive circuit when the output of therecording/reproduction mode control means designates reproducingoperation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing construction of a first embodiment of theinvention.

FIG. 2 is a diagram showing construction of a second embodiment of theinvention.

FIG. 3 is a diagram showing construction of a PLL in the secondembodiment.

FIG. 4 is a diagram showing behavior of crosstalk of a recording clockwith a reproduction system.

FIG. 5 is a diagram showing operation timings in the first embodiment.

FIG. 6 is a diagram showing operation timings in the second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereunder withreference to the drawings.

(1) First Embodiment

(1. 1) Construction of First Embodiment

Construction of the first embodiment of the present invention is shownin FIG. 1.

A semiconductor laser drive circuit 1 drives a semiconductor laser diode2 and an LD output light beam 3 is emitted to an optical disk (notshown) representing a recording medium. A disk reflection light beam 4representing a reflected light beam of the LD output light beam 3emitted to the optical disk is detected by photodetectors 51 of aphotoelectric conversion circuit 5 and current signals corresponding toa quantity of the reflected light beam are generated. Output currents ofthe photodetectors 51 are converted into voltage signals by means of I-Vamplifiers 52 of the photoelectric conversion circuit 5. Thephotoelectric conversion circuit 5 delivers the voltage signals asoutput signals (Va, Vb . . . Vh). Wired in a flexible cable 6 arecontrol signal lines of a digital signal processor (DSP) 7 forcontrolling the semiconductor laser drive circuit 1 and output signallines of the photoelectric conversion circuit 5. A read channel circuit8 processes the voltage signals from the photoelectric conversioncircuit 5 and supplies them to the DSP 7.

The semiconductor laser drive circuit 1 has LD recording drive currentwaveform generating means 11 for generating a semiconductor laser drivecurrent waveform during recording on the basis of a binary recordingsignal NRZ, a control signal WRgate for control of arecording/reproducing operation mode and a clock signal CLK, a serialinterface circuit 16 for supplying drive waveform information 17necessary for generation of the semiconductor laser drive waveform tothe LD recording drive current waveform generating means 11, a read APCamplifier 12 for current amplification of a drive current Lin suppliedfrom the DSP 7, a high frequency modulation circuit (HFM) 13 forsupplying a high frequency current to the semiconductor laser 2 duringreproduction, and adder means 14 for adding output currents of the LDrecording drive current waveform generating means 11, read APC amplifier12 and HFM 13 and supplying the sum to the semiconductor laser diode 2.

The DSP 7 has recording clock supply means 72 a for supplying arecording clock to the semiconductor laser drive circuit 1,recording/reproduction mode control means 71 for controlling the mode ofrecording/reproducing operation of the semiconductor laser drive circuit1, and clock stop means 73 for stopping the supply of the recordingclock signal CLK from the recording clock supply means 72 a to thesemiconductor laser drive circuit when the output signal WRgate of therecording/reproduction mode control means 71 designates the reproductionmode. Also, the DSP 7 supplies to the serial interface circuit 16 an SENsignal for rendering the serial interface circuit 16 operative, a clocksignal SCLK for the serial interface circuit 16 and a data signal SDIOfor the serial interface circuit 16 so as to control the serialinterface circuit 16.

The semiconductor laser drive circuit 1, semiconductor laser diode 2 andphotoelectric conversion circuit 5 are carried on an optical pickup. Theoptical pickup can be moved in a radial direction of the optical disk incompliance with a recording position (address) and a reproductionposition (address) when recording or reading on or from the optical diskis carried out. The control signals for the semiconductor laser drivecircuit 1 are supplied from the DSP 7 through the flexible cable 6 asdescribed previously. The output signals of the photoelectric conversioncircuit 5 are supplied to the read channel circuit 8 through theflexible cable 6 as described previously.

(1. 2) Operation of First Embodiment

Operation of the first embodiment and details of each component will bedescribed hereunder.

Operation of an optical disk apparatus of the present embodiment iscontrolled by the output signal WRgate of the recording/reproductionmode control means 71. When the control signal WRgate is L (recordingmode designation), recording operation is effected and when H(reproduction mode designation), reproducing operation is effected.

(1. 2. 1) Generation of Control Signal WRgate

The control signal WRgate is generated by the DSP 7 on the basis of aPID (Physical Identification Data) section detecting signal, which isdetected by the read channel circuit 8 on the basis of the outputsignals of the photoelectric conversion circuit 5 and delivered out ofthe read channel circuit 8, and a wobble signal due to wobble of therecording track.

A detailed description is given of a method for detection of the PIDsection and wobble signal in literature (1): NIKKEI ELECTRONICS (lastvolume), 1997.10.20 (no. 701), pages 178 to 182 fully explained by aplanner of the whole aspect of DVD-RAM standards and in FIGS. 17 to 20of the literature. The literature (1) describes the PID section as aheader section and the PID section detecting signal as an addressdetection signal.

In the case of a DVD-RAM (2.6 Gbyte) format, the PID is divided into twoas shown in FIG. 20 of the literature, the first half (headers 1, 2)being so disposed as to be ½ track width displaced toward the outerperiphery (or inner periphery) from the recording track (data recordingarea) and the second half (headers 3, 4) being so disposed as to be ½track width offset toward the inner periphery (or outer periphery). Therecording track (data recording area) is formed in a wobble form and thewobble proceeds at a cycle of 232 cycle ({fraction (1/186)} of chCLKperiod) per sector.

Accordingly, the tracking signal (push-pull signal) generated on thebasis of the output signal of the reproduction circuit system 5 varieslargely at the PID section. For example, on the assumption that theouter periphery side is + side, a large variation toward the + sideoccurs during the first half of the PID and a large variation toward the− side occurs during the second half. This behavior is indicated in FIG.20 of the literature. By utilizing the variation, the PID section isdetected. Since the recording track wobbles, the wobble is equivalent toan error in the tracking signal, enabling the wobble signal to bedetected.

The DSP 7 generates the control signal WRgate on the basis of the PIDsection detecting signal and a chCLK signal generated by n-multiplyingof the wobble signal.

Prior to a sequential recording operation of a plurality of sectors, thecontrol signal WRgate is first conditioned for reproduction to performdetection of the aforementioned PID section and detection of the currentaddress, address detection of PID is carried out until a desired sectorand after the desired sector has been detected, the control signalWRgate is conditioned for recording at recording data areas as shown at(2) in FIG. 5. Start and termination timings for the recording data areaof each sector are determined on the basis of a coefficient of the chCLKsignal generated from the previously-described wobble signal.

(1. 2. 2) Reproducing Operation

Reproducing operation is effected when the output signal WRgate of therecording/reproduction mode control means 71 is at a logical high (H).At that time, in the semiconductor laser drive circuit 1, the read APCamplifier 12 current-amplifies the reproduction drive current Iinsupplied from the DSP 7 through the flexible cable 6 and a resultingcurrent is added with a high frequency current signal from the highfrequency multiplexing circuit 13 by means of the adder means 14 todrive the semiconductor laser diode 2. The semiconductor laser diode 2is caused to luminesce by reproduction power so as to illuminate theoptical disk. Reflection light beam 4 from the optical disk is guided tothe photodetectors 51 and each of the photodetectors (a to h totaling to8) detects a quantity of reception light. Currents corresponding to thereception light quantities of the individual photodetectors aresubjected to current-to-voltage conversion by means of the I-Vamplifiers (a to h totaling to 8 circuits) corresponding to thephotodetectors and resulting voltages (detection signals Va to Vh in theFigure) are supplied to the read channel circuit 8 through the flexiblecable 6.

(1. 2. 3) Recording Operation

Recording operation is effected when the output signal WRgate of therecording/reproduction mode control means 71 is at a logical low (L).

At that time, in the semiconductor laser drive circuit 1, the recordingdrive current from the LD recording drive current generating means 11 isadded with the drive current of the read APC amplifier 12 (the samecurrent as the reproduction drive current during reproducing operation)at the adder circuit 14 so as to drive the semiconductor laser diode 2.

The LD recording drive current generating means 11 generates a recordingdrive current waveform corresponding to a length of a mark to berecorded (mark length being, for example, 3T, 4T, . . . , 11T) and alength of an adjoining space (space length being, for example, 3T, 4T, .. . , 11T) on the basis of the binary recording signal NRZ and clocksignal CLK (in the first embodiment, corresponding to a channel clocksignal, that is, corresponding to the period of a minimum unit of changeof the NRZ signal). What type of recording drive current waveform is tobe formed is set by the recording drive waveform information 17 suppliedfrom the DSP 7 through the serial interface 16.

(1. 2. 4) Operation Timings

In FIG. 5, operation timings in the first embodiment are shown. In theFigure, a format of the optical disk (disk format) is depicted at (1), asignal waveform of the control signal WRgate is depicted at (2), andsections (timings) at which the recording drive current waveform (writepulse) is delivered out of the LD recording drive current generatingmeans 11 or adder circuit 14 are depicted at (3). Further, in theFigure, sections (timings) at which the recording clock signal CLK issupplied to the semiconductor laser drive circuit 1 through the flexiblecable 6 are depicted at (4), a section (timing) at which the drivecurrent Iin is delivered is depicted at (5) and sections at which thePID (physical ID recorded with physical address information of eachsector) is reproduced and the output signals (Va, Vb . . . Vh) of therespective I-V amplifiers 52 are supplied to the read channel circuit 8through the flexible cable 6 are depicted at (6).

Like the DVD-RAM disk, for example, this disk format has a unit ofrecording defined by a sector unit and each sector includes a field(user data area (DATA rewritable) having a length of about 2418×16T) forrecording 2048-byte user data and an error correction sign, an area (PIDhaving a length of 128×16T) on which physical address information on thedisk of each sector is recorded (in the form of pits) in advance and anarea (GAP being, more strictly, comprised of a gap and a guard area andhaving a length of about 30×16T) serving as a buffer area between thetwo areas.

When user data is recorded on the sector N, the PID of the sector N isreproduced to confirm a physical address of the sector to be recordedwith data and thereafter recording is carried out. This aims atpreventing data from being recorded on an erroneous sector and data,already recorded, from being destroyed and lost in the case of thescheme capable of recording at random in a unit of sector (this realizesthe capability of random access in recording and reproduction inherentin the optical disk) in contrast to the conventional scheme forsequential data recording (for example, the recording method such asCD-R). So to speak, even in the recording mode, in addition to mereeffectuation of recording, recording of data and reproduction of PID arerepeated.

In compliance with the disk format described above, therecording/reproduction mode control means 71 delivers, as shown at (2)in the Figure, a control signal WRgate which designates the reproductionmode (read) at the PID section and the recording mode (write) at the GAParea and user data area (“DATA rewritable” at (1) in the Figure).

The clock stop means 71 responds to the mode designated by the controlsignal WRgate to control the supply/stop of the recording clock CLK tobe supplied to the semiconductor laser drive circuit 1. As shown at (4)in the Figure, the supply of the recording clock CLK is stopped when theWRgate is H (reproduction mode) and the recording clock CLK is suppliedwhen L (recording mode).

The LD recording drive current waveform generating means 11 generates arecording drive current waveform on the basis of the supplied recordingclock CLK and binary recording signal NRZ and the generated waveform isthen added with the drive current Iin, thereby driving (out write pulse)the semiconductor laser diode 2 at timings (user data area) shown at (3)in the Figure to form mark and space on the disk.

In the operation timings as above, during a period for delivery of theoutput signal shown at (6) in the Figure, that is, during the PIDreproduction period, the delivery of the recording clock CLK is stopped,with the result that the influence of EMI of the recording clock uponthe drive current Iin and output signals (Va, Vb . . . Vh) can bedecreased as compared to the case where the delivery of the recordingclock CLK keeps and as compared to the case where the delivery of thebinary recording signal NRZ keeps (out write pulse).

(1. 3) Effects of First Embodiment

As described above, in the first embodiment, the recording clock CLK isstopped during PID reproduction to bring about the following effects.

a) Since crosstalk of the recording clock CLK due to EMI with the outputsignals (Va, Vb . . . Vh) of the photoelectric conversion circuit 5 canbe reduced on the flexible cable 6, the error rate of data reproductionsuch as PID can be reduced.

b) Crosstalk of the recording clock CLK due to EMI with the drivecurrent Iin determining the drive current for the semiconductor laserdiode during reproduction can be reduced on the flexible cable 6,variation due to the crosstalk in the output light beam of thesemiconductor laser diode 2 can be reduced and consequently, S/Ndegradation in the reproduction signal can be prevented to therebyreduce the error rate of data reproduction such as PID.

c) Since the crosstalk of the recording clock with the reproductionsignal system can be reduced on the flexible cable 6 as described above,the recording clock signal, reproduction circuit system output signalsand drive current signal Iin can be arranged in close proximity to eachother on the flexible cable and the width of the flexible cable can bereduced to permit reduction in size of the apparatus.

(2) Second Embodiment

(2. 1) Construction of Second Embodiment

Construction of a second embodiment of the present invention is shown inFIG. 2. Components having the same function as those in FIG. 1 aredesignated by the same reference numerals.

Structurally, the present embodiment differs from the optical diskapparatus according to the first embodiment in that there is providedmultiplying means (phase locked loop) 15 for multiplying a clock signalCLK supplied by way of the clock stop means 73 to generate a channelclock signal chCLK and supplying it to the LD recording drive currentwaveform generating means 11.

Construction of the multiplying means (PLL) 15 is shown in FIG. 3. Afrequency division circuit 151 n-divides the frequency of the outputsignal chCLK of a VCO (voltage controlled oscillator) 156. A phasedifference detection circuit 152 detects a phase difference between anoutput signal CLKO of the frequency division circuit 151 and therecording clock signal CLK supplied by way of the clock stop means 73. Acharge pump circuit 153 generates a voltage)corresponding to thedetected phase difference of the phase difference detection circuit 152.An LPF (low-pass filter) 154 smooths the output signal of the chargepump circuit 153. A hold circuit 155 holds an output value of the LPF154 when the control signal WRgate is H (reproduction mode). The VCO 156changes its oscillation frequency in compliance with the output value ofthe LPF 154 supplied through the hold circuit 155. The output signal ofthe VCO 156 is supplied as the channel clock signal chCLK to the LDrecording drive current waveform generating means 11.

(2. 2) Operation of Second Embodiment

A multiplying number n of the multiplying means (PLL) 15 is set by theDSP 7 through the serial interface 16. Recording clock supply means 72 bresponds to the multiplying number n information 18 to deliver arecording clock CLK having a frequency which is 1/n of the frequencyfchCLK of the channel clock chCLK. The multiplying means (PLL) 15generates the channel clock chCLK by n-multiplying the frequency of therecording clock CLK and supplies it to the LD recording drive currentwaveform generating means 11. The LD recording drive current waveformgenerating means 11 generates a recording drive current waveform on thebasis of the binary recording signal NRZ and the channel clock signalchCLK supplied from the multiplying means (PLL) 15. Then, the thusgenerated current is added with the drive current Iin to drive thesemiconductor laser driver 2

(2. 2. 1) Operation Timings

Operation timings in the second embodiment are shown in FIG. 6. In thefigure, a format of the optical disk (disk format) is depicted at (1) inFIG. 6, the control signal WRgate is depicted at (2) in FIG. 6 andsections (timings) at which the recording drive current waveform (writepulse) is delivered out of the LD recording drive current waveformgenerating means 11 or adder circuit 14 are depicted at (3) in FIG. 6.These are the same as the operation timings in the first embodiment. Inthe Figure, a timing for operation of the multiplying means (PLL) 15 isdepicted at (4) in FIG. 6 and sections (timings) at which the recordingclock CLK (in the second embodiment, the frequency of the CLK is 1/n ofthe channel clock chCLK) is supplied to the semiconductor laser drivecircuit 1 through the flexible cable 6 are depicted at (5) in FIG. 6. Inthe Figure, a section (timing) at which the drive current Iin isdelivered is depicted at (6) in FIG. 6 and sections (timings) at whichthe PID is reproduced and the output signal of each I-V amplifier 52 issupplied to the read channel circuit 8 through the flexible cable 6 aredepicted at (7) in FIG. 6.

When user data is recorded in a sector unit, like the first embodiment,the recording/reproduction mode control means 71 renders the controlsignal WRgate H (reproduction mode) at the PID sections and renders it L(recording mode) at the GAP and user data area.

Like the first embodiment, the clock stop means 73 stops the supply ofthe recording clock CLK from the recording clock supply means 72 b tothe semiconductor laser drive circuit 1 when the WRgate is H(reproduction mode) and supplies the recording clock CLK to thesemiconductor laser drive circuit 1 when the WRgate is L (recordingmode).

When the control signal WRgate is L (recording mode), the multiplyingmeans (PLL) 15 receives, as an input signal, the recording clock CLKsupplied through the clock stop means 73 as shown at (4) in FIG. 6 andoperates to cause the phase of the input signal to coincide with that ofthe output signal CLKO of the frequency division circuit 151. With thephases of the two rendered to be coincident with each other, the outputof the VCP 156 consequently becomes the channel clock chCLK which is ntimes the CLK and the channel clock is supplied to the LD recordingdrive current waveform generating means 11. When the control signalWRgate is H (reproduction mode), the hold circuit 155 holds animmediately preceding (immediately before the change of the WRgate fromL to H) output value of the LPF 154.

The oscillation frequency of the VCO 156 is controlled by the outputvalue of the hold circuit 155. Accordingly, during the section at whichthe WRgate is H (reproduction mode), the supply of the recording clockCLK is stopped but the oscillation frequency of the VCO 156 holds afrequency which is substantially equal to the frequency when the WRgateis L (recording mode).

By holding the oscillation frequency of the VCO 156 at the PIDreproduction section, pull-in of the VCO 156 to the recording clock CLK(operation to cause the frequency division circuit output CLKO tocoincide with the frequency of the recording clock CLK and to make thephases coincident with each other) can be effected more speedily whenthe WRgate again comes into L (recording mode). The reason for this isthat the held frequency of the VCO 156 is close to n times the recordingclock CLK, in other words, the frequency of the output CLKO of thefrequency division circuit nearly equals the frequency of the recordingclock CLK and therefore the control time for making the frequency of theCLKO coincident with the frequency of the CLK can be shortened.

Since at the operation timings as above the delivery of the recordingclock CLK is stopped during the period shown at (6) in the Figure inwhich the output signal is delivered, that is, during the PIDreproduction period as in the case of the first embodiment, theinfluence of the recording clock due to EMI upon the drive current Iinand output signals (Va, Vb . . . Vh) can be reduced as compared to thecase where the delivery of the recording clock CLK keeps and to the casewhere the delivery of the binary recording signal NRZ keeps (out writepulse).

Further, the frequency of the recording clock CLK passing on theflexible cable 6 can be reduced as compared to that in the firstembodiment and consequently, the influence of the recording clock CLKdue to EMI can be reduced by itself.

(2. 3) Effects of Second Embodiment

As described above, in the second embodiment, the following effects canbe brought about in addition to those attained by the first embodiment.

d) Since the recording clock CLK is n-multiplied on the side of thesemiconductor laser drive circuit 1 (optical pickup side) by means ofthe multiplying means (PLL) 15, the frequency of the recording clock CLKon the flexible cable 6 can be reduced to 1/n. Accordingly, the level ofunwanted radiation (EMI) emitted from the flexible cable 6 can bereduced as compared to that in the first embodiment, so that crosstalkwith the drive current Iin during data recording can be reduced ascompared to that in the first embodiment. Namely, the recording drivecurrent waveform can be generated with higher accuracy in the presentembodiment than in the first embodiment.

e) By holding the oscillation frequency of the VCO 156 at thereproduction mode section, the oscillation frequency of the VCO 156 canbe pulled in to n times the frequency of the recording clock CLK morespeedily at the time that the recording mode starts, with the resultthat variation of the channel clock chCLK at the user data area can bereduced to thereby prevent degradation of reliability of the recordingdata.

Industrial Applicability

In the optical disk apparatus of the present invention, S/N degradationin the reproduction signal can be reduced. Further, an increase in theEMI level which causes the S/N degradation in the reproduction signalcan be suppressed.

Especially, in an optical disk apparatus in which recording of data iscarried out by reading address information on the optical disk andconfirming the recording position, the error rate of reproduction ofdata such as address information can be reduced and hence reliability ofdata recording can be promoted.

What is claimed is:
 1. An optical disk apparatus comprising: a flexiblecable; a semiconductor laser drive circuit, connected to the flexiblecable, including: laser drive (LD) recording drive current waveformgenerating means for generating a recording drive current waveform for asemiconductor laser based on a clock signal and a mark lengthinformation when recording information on a recording medium, andreproduction drive current supply means for supplying a reproductiondrive current to the semiconductor laser when reading information fromthe recording medium; recording clock supply means, connected to theflexible cable, for supplying the clock signal to the semiconductorlaser drive circuit through the flexible cable; signal processing means,connected to the flexible cable, for supplying mark length informationrepresenting information to be recorded on the recording medium to thesemiconductor laser drive circuit through the flexible cable;recording/reproduction mode control means for controlling arecording/reproduction operation of the semiconductor laser drivecircuit; and clock stop means for stopping the clock signal from beingsupplied from the recording clock supply means to the semiconductorlaser drive circuit when an output of the recording/reproduction modecontrol means designates a reproduction operation; wherein the clockstop means starts supplying the clock signal for recording informationon the recording medium after the recording/reproduction mode controlmeans designates a recording operation and before the laser drive (LD)recording drive current waveform generating means generates therecording drive current waveform.
 2. An optical disk apparatus accordingto claim 1, wherein: the signal processing means also supplies drivewaveform information to the semiconductor laser drive circuit throughthe flexible cable; and the laser drive (LD) recording drive currentwaveform generating means generates the recording drive current waveformfor the semiconductor laser based on the mark length information, theclock signal, and the drive waveform information.
 3. An optical diskapparatus according to claim 1, further comprising an optical pickup tosupport the semiconductor laser drive circuit.
 4. An optical diskapparatus comprising: a flexible cable; a semiconductor laser drivecircuit, connected to the flexible cable, including: multiplying meansfor generating a second clock signal having a frequency which is n timesa frequency of a first clock signal (n being a positive integer), laserdrive (LD) recording drive current waveform generating means forgenerating a recording drive current waveform for a semiconductor laserbased on the second clock signal and a mark length information, whenrecording information on a recording medium, and reproduction drivecurrent supply means for supplying a reproduction drive current to thesemiconductor laser, when reading information from the recording medium;recording clock supply means, connected to the flexible cable, forsupplying the first clock signal to the semiconductor laser drivecircuit through the flexible cable; signal processing means, connectedto the flexible cable, for supplying mark length informationrepresenting information to be recorded on the recording medium to thesemiconductor laser drive circuit through the flexible cable;recording/reproduction mode control means for controlling arecording/reproduction operation of the semiconductor laser drivecircuit; and clock stop means for stopping the first clock signal frombeing supplied from the recording clock supply means to thesemiconductor laser drive circuit when an output of therecording/reproduction mode control means designates a reproductionoperation; wherein the clock stop means starts supplying the first clocksignal for recording information on the recording medium after therecording/reproduction mode control means designates a recordingoperation and before the laser drive (LD) recording drive currentwaveform generating means generates the recording drive currentwaveform.
 5. An optical disk apparatus according to claim 4, wherein:the signal processing means also supplies drive waveform information tothe semiconductor laser drive circuit through the flexible cable; andthe laser drive (LD) recording drive current waveform generating meansgenerates the recording drive current waveform for the semiconductorlaser based on the mark length information, the second clock signal, andthe drive waveform information.
 6. An optical disk apparatus accordingto claim 5, further comprising an optical pickup to support thesemiconductor laser drive circuit.
 7. An optical disk apparatusaccording to claim 4, wherein the multiplying means includes: phasedifference detection means for detecting a phase difference between thefirst clock signal and the second clock signal; a VCO having a variableoscillation frequency which changes in accordance with the phasedifference detected by the phase difference detection means; and holdmeans for holding the oscillation frequency of the VCO at an oscillationfrequency prevailing immediately before a beginning of the reproductionoperation when the output of the recording/reproduction mode controlmeans designates the reproduction operation.
 8. An optical diskapparatus according to claim 7, further comprising an optical pickup tosupport the semiconductor laser drive circuit.
 9. An optical diskapparatus according to claim 4, further comprising an optical pickup tosupport the semiconductor laser drive circuit.
 10. An optical diskapparatus constructed to supply signals for controlling a semiconductorlaser drive circuit carried on an optical pickup from a signalprocessing circuit to the semiconductor laser drive circuit through aflexible cable; wherein the semiconductor laser drive circuit isconstructed to generate a drive current signal for a semiconductor laserbased on a binary signal representing data to be recorded using theoptical pickup and a clock signal which are supplied from the signalprocessing circuit to the semiconductor laser drive circuit through theflexible cable; and wherein the signal processing circuit is constructedto stop supplying the clock signal to the semiconductor laser drivecircuit through the flexible cable during reproduction of data, and tostart supplying the clock signal to the semiconductor laser drivecircuit through the flexible cable before recording of data.
 11. Anoptical disk apparatus according to claim 10, wherein: drive waveforminformation is supplied from the signal processing circuit to thesemiconductor laser drive circuit through the flexible cable; and thesemiconductor laser drive circuit is constructed to generate the drivecurrent signal for the semiconductor laser based on the binary signal,the clock signal, and the drive waveform information which are suppliedfrom the signal processing circuit to the semiconductor laser drivecircuit through the flexible cable.
 12. An optical disk apparatusaccording to claim 10, wherein the semiconductor laser drive circuit isconstructed to generate a drive current signal for the semiconductorlaser during data recording based on the binary signal, the clocksignal, and a drive current signal for the semiconductor laser duringdata reproduction which is supplied from the signal processing circuitto the semiconductor laser drive circuit through the flexible cable. 13.An optical disk apparatus according to claim 10, wherein thesemiconductor laser drive circuit is constructed to generate the drivecurrent signal for the semiconductor laser based on a multiplied clocksignal obtained by multiplying by n times a frequency of the clocksignal supplied from the signal processing circuit to the semiconductorlaser drive circuit through the flexible cable (n being a positiveinteger).
 14. An optical disk apparatus according to claim 10, whereinaddress information recorded on an optical disk is reproduced to confirma recording position on the optical disk, and thereafter data isrecorded on the optical disk.
 15. An optical disk apparatus constructedto supply a signal for controlling a semiconductor laser drive circuitcarried on an optical pickup from a signal processing circuit to thesemiconductor laser drive circuit through a flexible cable; wherein thesemiconductor laser drive circuit is constructed to generate a drivecurrent signal for a semiconductor laser based on a binary signalrepresenting data to be recorded using the optical pickup and a clocksignal which are supplied from the signal processing circuit to thesemiconductor laser drive circuit through the flexible cable; andwherein the signal processing circuit is constructed to stop supplyingthe clock signal to the semiconductor laser drive circuit through theflexible cable during reproduction of data, and to supply the clocksignal to the semiconductor laser drive circuit through the flexiblecable before a period in which the binary signal is supplied from thesignal processing circuit through the flexible cable.
 16. An opticaldisk apparatus according to claim 15, wherein: drive waveforminformation is supplied from the signal processing circuit to thesemiconductor laser drive circuit through the flexible cable; and thesemiconductor laser drive circuit is constructed to generate the drivecurrent signal for the semiconductor laser based on the binary signal,the clock signal, and the drive waveform information which are suppliedfrom the signal processing circuit to the semiconductor laser drivecircuit through the flexible cable.
 17. An optical disk apparatusaccording to claim 15, wherein the semiconductor laser drive circuit isconstructed to generate a drive current signal for the semiconductorlaser during data recording based on the binary signal, the clocksignal, and a drive current signal for the semiconductor laser duringdata reproduction which is supplied from the signal processing circuitto the semiconductor laser drive circuit through the flexible cable. 18.An optical disk apparatus according to claim 15, wherein thesemiconductor laser drive circuit is constructed to generate the drivecurrent signal for the semiconductor laser based on a multiplied clocksignal obtained by multiplying by n times a frequency of the clocksignal supplied from the signal processing circuit to the semiconductorlaser drive circuit through the flexible cable (n being a positiveinteger).
 19. An optical disk apparatus according to claim 15, whereinaddress information recorded on an optical disk is reproduced to confirma recording position on the optical disk, and thereafter data isrecorded on the optical disk.